<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="button" value="后退" onclick="history.back()">
</body>
</html>
<script type="text/javascript">
    var arr= [1,4,9]
    // arr[3] = 5
    // document.write(arr.length)
     var arr1 =[3,7,6]
     var tem= arr.concat(arr1)
    // document.write(tem.length)
    tem.sort();
    tem.reverse();
    for (var i = 0; i < tem.length; i++) {
        document.write(tem[i]+"<br>")
    }
    // function back() {
    //     history.back();
    // }

</script>